WASHINGTON (Reuters) - President Barack Obama's embattled
U.S. healthcare law, having survived a rollout marred by
technology failures, reaches a milestone on Monday with the end
of its first enrollment wave, and with the administration likely
to come close to its goal of signing up 7 million people in
private health insurance.

But as the White House and its allies declare victory, major
hurdles remain. And it will take years to determine whether the
law will accomplish its mission of creating stable insurance
markets that can help a significant number of America's nearly
50 million uninsured gain health coverage, experts say.

Republicans are counting on that uncertainty to play into
their strategy for the midterm congressional elections in
November. Their plan: Draw on public dissatisfaction with the
Patient Protection and Affordable Care Act to help the GOP win
control of the U.S. Senate and retain the party's dominance in
the House of Representatives.

"We're not really going to know whether it worked or not
until the third or fourth year. And of course, that's two
elections down the road," said Timothy Jost, a professor at the
Washington and Lee University School of Law in Lexington,
Virginia.

"What I worry about is that we won't be able to figure out
whether it's worked or not until it's too late," he said.

Even before the first enrollment period comes to a close,
Republicans and some Democrats have separately proposed election
year changes that could appeal to voter concerns - and would
leave the law substantially altered.

Republican proposals would undermine Obamacare by making
health insurance optional and returning sick people to high-risk
pools. A handful of Senate Democrats last week also proposed
some Republican-sounding ideas that would allow insurance to be
sold across state lines, discontinue the employer mandate for
many small businesses and allow low-premium, high-deductible
plans to be sold in the marketplaces.

Families USA, an administration ally on healthcare reform,
plans to make its own public recommendations this week on how
the enrollment drive for 2015 might be improved. "Our
recommendations will build on the laudatory success of the
first enrollment period," said Ron Pollack, the group's
executive director.

'PROOF OF CONCEPT'

So far, enrollment has been uneven. About half the states
are expanding Medicaid as the law intended, and interest in
private insurance lags in more than a dozen states where public
leaders oppose Obamacare or have failed to produce a working
state-operated marketplace. Consumer costs next year could vary
widely, with premiums likely to rise in the double-digit
percentages in states with lower enrollment.

"In most of the country, they've basically done a proof of
concept: It can work. It has not yet succeeded and won't succeed
until you know that most of the uninsured have been covered and
the market's stable, with reasonable growth in premiums," said
Larry Levitt, a health policy expert at the nonpartisan Kaiser
Family Foundation.

The nonpartisan Congressional Budget Office estimates that
14 million people will obtain health coverage this year through
the private insurance marketplaces or the expansion of the
Medicaid program for the poor. However, coverage is not expected
to hit its peak of 37 million people until 2018, when the CBO
forecasts 25 million people in the marketplaces and 12 million
enrolled through Medicaid or its sister health plan, the
Children's Health Insurance Program.

Over the next year the administration plans to fully link
its enrollment website, HealthCare.gov, with the insurance
industry for sign-ups and payments. The administration still has
no automated systems for confirming enrollment data,
distributing subsidies or compensating insurers for unexpected
losses.

There are signs of a last-minute enrollment surge by younger
adults for 2014 that could help keep the new online marketplaces
viable for insurers. Hospitals and doctor practices are also
introducing changes to the way they provide healthcare in line
with the law.

"The Affordable Care Act is here to stay. It's the framework
that everybody in the healthcare industry is working within and
developing their strategic plans around," said Dr. Ezekiel
Emanuel, who was a top White House adviser on healthcare during
the law's development.

"Even the opposition, the Republicans, recognize the ACA is
the law of the land, and despite the rhetoric, actually accept
it," he said.

Many of the newly insured are ready to declare the law's
benefits. Barbara Doucet, 63, of Newnan, Georgia, says she can
afford health insurance for the first time in 14 years and no
longer worries about what might happen should she have an
accident or become seriously ill.

"I was scared constantly, absolutely terrified that
something would happen and what would I do. I didn't sleep
really well for a long, long, long, long time," Doucet, a
waitress and reform advocate, told Reuters in an interview
arranged through Consumers Union, a public advocacy group that
sees Obamacare as a benefit to consumers.

"I'm extremely pleased with ACA, I really am," she said.

Stories like Doucet's clash with tales of people who find
insurance more expensive because of Obamacare's expanded
coverage requirements.

Amy Newbold, a 57-year-old saleswoman from Randolph County,
North Carolina, lost her employer insurance last year.

Through HealthCare.gov, she found a mid-tier "silver" plan
with premiums that at first blush are $75 a month lower than her
previous policy. But there are no savings, she says, since her
old premiums were paid with pretax dollars and Obamacare
premiums are paid with aftertax dollars. Newbold said she faces
substantially higher drug costs for arthritis and psoriasis and
worries that an out-of-pocket maximum of $5,000 could put needed
medicines out of reach.

"I feel left out in the cold, and I don't know why it has to
be that way," she said in an interview arranged through the
office of Republican U.S. Representative Renee Ellmers, an
Obamacare opponent from North Carolina.

'IMPROVING' THE LAW

If Republicans seize the Senate from Democrats, Obama may be
forced to compromise on key aspects of the law, including
requirements that most individuals obtain coverage and that
employers with 50 or more workers offer health coverage, two of
its most unpopular provisions.

Polls show most Americans would prefer to see Obamacare
changed, not repealed. In a March survey from the Kaiser Family
Foundation, most Americans dislike the law, but 59 percent
wanted it retained or improved.

That could make Republicans think twice about pushing for
repeal. But analysts say big changes may still be likely.

Some key features of the law are likely to endure, they say,
pointing to the ban on higher costs for people with preexisting
medical conditions and new medical business models that
discourage costly fee-for-service medicine by putting a priority
on patient outcomes and cost savings.

Analysts say Republicans could also scale back marketplace
subsidies to help low-income consumers buy insurance, pricing
restrictions on insurers and taxes intended to help fund the
reform effort. And they predict that if Democrats are chastened
by losses in the congressional elections, they might be more
inclined to back some Republican proposals.

"Republicans will make changes. It's not a question of 'if.'
It's a question of how many," said James Capretta, a health
policy expert with the conservative Ethics & Public Policy
Center.